Hearing instruments or hearing aids comprises at least one microphone for receipt of incoming sound such as speech and music. The incoming sound is amplified and processed in a signal processor of the hearing instrument in accordance with one or more preset listening program(s) that typically have been computed from a user's specific hearing deficit for example expressed in an audiogram. An output amplifier delivers the processed sound signal to the user's ear canal via a miniature speaker or receiver that may be housed in a casing of the hearing instrument together with the microphone or separately in an ear plug.
Modern hearing instruments are furthermore providing increasingly sophisticated signal processing functions and user interface functions thanks to rapid progress of digital integrated circuit technology and algorithm development in digital signal processing. Hence, modern hearing instruments typically include a plurality of different listening programs that may utilize various microphone signals as audio input or so-called direct audio input sources delivered e.g. through RF antennas, infrared receivers or magnetic antennas like a telecoil. Furthermore, a modern hearing instrument often includes more than one microphone for example 2, 3 or 4 microphones that may be simultaneously operative under certain conditions to deliver multiple microphone signals. The multiple microphone signals may be exploited to provide various types of noise reduction and beam-forming functions or algorithms. One of the multiple microphone signals may be generated by an ear canal microphone and used for an occlusion suppression function for example as disclosed in U.S. Pat. No. 8,520,875. The selected type and number of signal processing functions are typically associated with a particular listening program that is either selected automatically by a control and processing circuit of the hearing instruments or selected manually by the hearing instrument user via appropriate user actuable control buttons. Hence, a particular listening program will often utilize a specific signal processing function or set of functions that are tailored to particular sound environment of the user. A first listening program may for example comprise a beam-forming function or algorithm and be tailored to noisy sound environments such as a train station or a bar. A second listening program may utilize a single omnidirectional microphone input signal and be tailored to a relatively quiet home or office sound environment etc.
However, a hearing aid microphone consumes a certain amount of power when the microphone is operative to produce a useful microphone signal from the impinging sound such as between about 20 mW and 50 mW. This power consumption is drawn through positive and negative power supply terminals of the microphone that are coupled to a microphone supply voltage of the hearing instrument. The current drawn from the microphone supply voltage depletes the often modest energy capacity of a battery source or cell of the hearing instrument. The power consumption of the hearing aid microphone is typically drawn by various kinds of preamplifiers and other signal processing circuitry housed inside a capsule or housing of the hearing aid microphone. In view of the limited amount of energy stored in typical hearing instrument battery cells, it is desirable to reduce the power consumption of hearing instrument circuitry and components where and whenever possible.
U.S. Pat. No. 6,760,457 B1 discloses a hearing aid with a magnetically activated switch that automatically switches the hearing aid input from a microphone input to a voice coil input in response to the presence of a magnetic field. The magnetic field may be generated by a magnet in a telephone handset such that the hearing instrument automatically switches to voice coil input when the hearing aid user picks up the handset for answering the telephone.